Stimulated Emission\nand Lasing from Bulk CdSe Nanocrystals

Nanocrystals with a size in the regime of vanishing quantum\nconfinement,\nor bulk nanocrystals (BNCs), have emerged recently as viable solution\nprocessable optical gain materials in the green part of the spectrum.\nHere, we show that these properties can be extended to the crucial\nred region using CdSe BNCs. Through quantitative time-resolved spectroscopy,\nwe can model these nanocrystals as bulk semiconductors, thereby revealing\nthat the gain originates from an unbound electron–hole plasma\nstate. The gain is broadband in nature and is not capped by Auger\nprocesses, but by a slower second-order recombination resulting in\nnanosecond gain lifetimes. Finally, optically pumped lasers under\nfemtosecond pulsed and quasi-continuous wave operation are demonstrated\nusing a photonic crystal surface emitting laser cavity, thereby stretching\nfrom 635 to 720 nm. Our results indicate that compositional variation\ncan indeed provide spectral versatility to the BNC concept, while\npreserving the excellent gain metrics associated with it.